1. Field of the Invention
The present invention relates to a storage device and a method for controlling the packet size of the storage device.
2. Description of the Related Art
Storage devices have disk drives such as hard disk drives arranged in the form of an array and provide storage regions on the basis of RAID (Redundant Arrays of Inexpensive Disks), for example. A host computer (‘host’, hereinbelow) accesses a logical storage region provided by a storage device that performs data reading/writing. A data transfer between a host and a storage device is executed in packet units. The packet size can be established as an integer multiple of a unit that can be read/written by means of a single access operation with respect to an access target volume (Japanese Patent Application Laid Open No. H5-242006).
Although the technology described in this document establishes the packet size between the storage device and host, the packet size within the storage device is in no way considered. For example, write data that is inputted from the host to the storage device, for example, is transmitted internally from a host interface to a disk drive interface and is then written from the disk drive interface to each disk drive. Conversely, read data that is read from each disk drive is transmitted internally from the disk drive interface to the host interface and then transferred from the host interface to the host.
Therefore, although a data transfer can also be made by using packets within the storage device, the packet size within the storage device is fixed in the same way. That is, the packet size in the storage device is fixed to suit the fastest communication environment irrespective of the communication environment (communication band or the like) between the storage device and the host.
Therefore, because packet sizes are different outside and inside the storage device, efficiency in cases where data switching is performed between these external packets is reduced and there is therefore a drop in the data transfer efficiency of the storage device.
In the case of a storage device, a variety of types of hosts known as so-called mainframe system hosts, open system hosts, and the like, for example, can be connected. Each of these hosts performs a data transfer with a storage device in accordance with the respective communication protocol of each host. Therefore, the communication environment between each of these types of hosts and the storage device differs from one type of host to the next. In cases where the packet size that is used in exchanges between the host and the storage device matches or is substantially equal to the packet size within the storage device, the data can be moved rapidly between internal and external packets. However, in cases where the internal and external packet sizes differ greatly, the data transfer efficiency drops.
Therefore, in the case of a storage device to which a variety of types of hosts can be connected at the same time, there is the possibility of a large discrepancy in the communication environment depending on the types of hosts. However, in the prior art, no consideration was paid to the diversity of the communication environments between such hosts and storage devices and the packet size within the storage device was set as fixed without variation.
Similar problems can arise between storage devices and memory drives. The data processing speed and so forth of memory drives differs according to the type. However, because a packet size that is fixed without variation has been used conventionally irrespective of the type of memory drive, there is a margin for improving the data transfer efficiency between memory drives and storage devices.